mm: convert partially_mapped set/clear operations to be atomic

Other page flags in the 2nd page, like PG_hwpoison and PG_anon_exclusive
can get modified concurrently.  Changes to other page flags might be lost
if they are happening at the same time as non-atomic partially_mapped
operations.  Hence, make partially_mapped operations atomic.

Link: https://lkml.kernel.org/r/20241212183351.1345389-1-usamaarif642@gmail.com
Fixes: 8422acd ("mm: introduce a pageflag for partially mapped folios")
Reported-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/all/e53b04ad-1827-43a2-a1ab-864c7efecf6e@redhat.com/
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Yu Zhao <yuzhao@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: uarif1

include/linux/page-flags.h

@@ -862,18 +862,10 @@ static inline void ClearPageCompound(struct page *page)
 	ClearPageHead(page);
 }
 FOLIO_FLAG(large_rmappable, FOLIO_SECOND_PAGE)
-FOLIO_TEST_FLAG(partially_mapped, FOLIO_SECOND_PAGE)
-/*
- * PG_partially_mapped is protected by deferred_split split_queue_lock,
- * so its safe to use non-atomic set/clear.
- */
-__FOLIO_SET_FLAG(partially_mapped, FOLIO_SECOND_PAGE)
-__FOLIO_CLEAR_FLAG(partially_mapped, FOLIO_SECOND_PAGE)
+FOLIO_FLAG(partially_mapped, FOLIO_SECOND_PAGE)
 #else
 FOLIO_FLAG_FALSE(large_rmappable)
-FOLIO_TEST_FLAG_FALSE(partially_mapped)
-__FOLIO_SET_FLAG_NOOP(partially_mapped)
-__FOLIO_CLEAR_FLAG_NOOP(partially_mapped)
+FOLIO_FLAG_FALSE(partially_mapped)
 #endif
 
 #define PG_head_mask ((1UL << PG_head))

mm/huge_memory.c

@@ -3577,7 +3577,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 		    !list_empty(&folio->_deferred_list)) {
 			ds_queue->split_queue_len--;
 			if (folio_test_partially_mapped(folio)) {
-				__folio_clear_partially_mapped(folio);
+				folio_clear_partially_mapped(folio);
 				mod_mthp_stat(folio_order(folio),
 					      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
 			}
@@ -3689,7 +3689,7 @@ bool __folio_unqueue_deferred_split(struct folio *folio)
 	if (!list_empty(&folio->_deferred_list)) {
 		ds_queue->split_queue_len--;
 		if (folio_test_partially_mapped(folio)) {
-			__folio_clear_partially_mapped(folio);
+			folio_clear_partially_mapped(folio);
 			mod_mthp_stat(folio_order(folio),
 				      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
 		}
@@ -3733,7 +3733,7 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
 	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
 	if (partially_mapped) {
 		if (!folio_test_partially_mapped(folio)) {
-			__folio_set_partially_mapped(folio);
+			folio_set_partially_mapped(folio);
 			if (folio_test_pmd_mappable(folio))
 				count_vm_event(THP_DEFERRED_SPLIT_PAGE);
 			count_mthp_stat(folio_order(folio), MTHP_STAT_SPLIT_DEFERRED);
@@ -3826,7 +3826,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 		} else {
 			/* We lost race with folio_put() */
 			if (folio_test_partially_mapped(folio)) {
-				__folio_clear_partially_mapped(folio);
+				folio_clear_partially_mapped(folio);
 				mod_mthp_stat(folio_order(folio),
 					      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
 			}